-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

=============================================================================
FreeBSD-EN-21:21.ipfw                                           Errata Notice
                                                          The FreeBSD Project

Topic:          Kernel panic with ipfw link-layer filtering enabled

Category:       core
Module:         ipfw
Announced:      2021-06-29
Affects:        FreeBSD 13.0
Corrected:      2021-06-19 14:08:49 UTC (stable/13, 13.0-STABLE)
                2021-06-29 17:09:43 UTC (releng/13.0, 13.0-RELEASE-p3)

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit
<URL:https://security.FreeBSD.org/>.

I.   Background

ipfw(4) is a IP packet filter implementation in the kernel.  It uses the
pfil(9) interface to hook into several 

II.  Problem Description

When link-layer filtering is enabled by setting the net.link.ether.ipfw
sysctl to 1, packets received by the filter may be reallocated to ensure
that protocol headers are contiguous in memory.  In this case, the old
copy of the packet is freed.  However, the filter failed to update the
pointer returned to the pfil(9) caller, resulting in the use of a
pointer to freed memory.

III. Impact

Systems which use ipfw(4)'s link-layer filtering capabilities may panic.

IV.  Workaround

No workaround is available.  Systems not using ipfw(4), or systems that
do not explicitly enable link-layer filtering by setting the
net.link.ether.ipfw sysctl to 1, are not affected.

V.   Solution

Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date and reboot.

Perform one of the following:

1) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the amd64, i386, or
(on FreeBSD 13 and later) arm64 platforms can be updated via the
freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for an erratum update"

2) To update your system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/EN-21:21/ipfw.patch
# fetch https://security.FreeBSD.org/patches/EN-21:21/ipfw.patch.asc
# gpg --verify ipfw.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

This issue is corrected by the corresponding Git commit hash or Subversion
revision number in the following stable and release branches:

Branch/path                             Hash                     Revision
- -------------------------------------------------------------------------
stable/13/                              ed1acef3fe30    stable/13-n246063
releng/13.0/                            4647d115ff84  releng/13.0-n244750
- -------------------------------------------------------------------------

For FreeBSD 13 and later:

Run the following command to see which files were modified by a
particular commit:

# git show --stat <commit hash>

Or visit the following URL, replacing NNNNNN with the hash:

<URL:https://cgit.freebsd.org/src/commit/?id=NNNNNN>

To determine the commit count in a working tree (for comparison against
nNNNNNN in the table above), run:

# git rev-list --count --first-parent HEAD

For FreeBSD 12 and earlier:

Run the following command to see which files were modified by a particular
revision, replacing NNNNNN with the revision number:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<other info on the problem>

<URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=254015>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-21:21.ipfw.asc>
-----BEGIN PGP SIGNATURE-----
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=pdU2
-----END PGP SIGNATURE-----
